It is now commonly accepted that the vision impairment disease known as cataracts can be alleviated by surgically replacing the natural lens of the eye with an artificial intraocular lens. The condition of cataracts is characterized by the clouding of the natural lens of the eye so that the amount of light which reaches the retina is substantially reduced or completely eliminated.
Surgical instruments utilizing ultrasonic vibrations in combination with the circulation of irrigation liquid over the operative site for the removal of tissue from a biological body are well-known and widely used, particularly in enclosed and substantially enclosed operative sites. Such surgical instruments are particularly well adapted for the removal of cataracts and other surgical procedures performed on the eye. Ultrasonic surgical instruments of the type with which the present invention is primarily concerned employ an elongated probe or hollow needle having an end threadedly attached through a vibration transmissive member or resonator to a transducer for supplying ultrasonic energy to the other or free end of the hollow needle. The ultrasonic energy is emitted to dislodge and breakup or emulsify tissue from the operative site for removal by aspiration. Irrigating fluid is delivered through the instrument into a shield, or sheath, surrounding the body of the needle for discharge adjacent to the tip or free end of the needle and is returned by suction through a hollow center in the tubular body of the needle.
An ultrasonic surgical aspirator of this type is shown in U.S. Pat. No. 3,805,787 as including conduits for applying suction through the center of the ultrasonically operative needle and for supplying irrigating fluid around the outer surface of the needle through a passage defined by a tubular shield. The irrigation fluid flows around the free end of the needle element and back through the center of the hollow needle to effectively irrigate and remove the discharged and emulsified tissue. Another such ultrasonic surgical aspirator is manufactured and sold by Storz Instrument Company, Model No. D-8110, located in St. Louis, Miss.
Significant attention in the art for improving the operative characteristics of these instruments for the convenience of the surgeon and to enhance the efficacy of the instrument for the safety of the patient has been directed to solving a number of problems. For example, it has been desired to utilize greater electrical power and circuitry to energize the transducer contained within the ultrasonic surgical instrument to obtain greater excursion or vibratory action of the needle probe. However, such increased power and vibratory action can create cavitation bubbles caused by the ultrasonically-vibrating member and as a result of directing the irrigating fluid past the vibrating connection or interface between the resonator and needle probe. The needle probes used in these instruments are generally standardized in the industry and typically include a standardized threaded portion at one end for attachment to the resonator or vibration transmissive member and a square shank portion immediately adjacent said threads for receiving a tool for securely attaching the needle probe to the ultrasonic instrument. It is believed that the cavitation bubbles are created in part by the ultrasonic energy being radiated into the irrigation fluid via the sharp angles of the resonator member and needle probe connection or interface site. These cavitation bubbles create a visual obstruction in delicate surgery, and an annoyance in the eye during surgery. Usually the surgeon is required to interrupt the surgery to permit the aspiration system to remove the bubbles before resuming the surgery.
One method of attempting to reduce cavitation bubbles in such an ultrasonic surgical instrument is shown in U. S. Pat. Nos. 4,681,561 and 4,816,017, both entitled "Ultrasonic Decoupling Sleeve". The decoupling sleeve attempts to define a new flow path within the irrigation fluid path existing within the ultrasonic surgical instrument. However, such a decoupling sleeve has been found to be ineffective in reducing cavitation bubbles occurring within such instruments.
Accordingly, it is desired to isolate the resonator/needle probe interface from the irrigation fluid present in the fluid path between the resonator/needle probe structures and the outer shield to avoid cavitation bubbles in the irrigation fluid path of the ultrasonic instrument.